1. Field of the Invention
The present invention relates to apparatus for soldering integrated circuits(ICs) and, more particularly, to apparatus for soldering ICs including a plurality of leads using two holding blocks by turns, and thereby reducing soldering time.
2. Description of the Related Art
The present invention will be more thoroughly understood by reference to a tape carrier package (TCP) type pentium processor.RTM. as an example of an IC.
The TCP type pentium processor.RTM. is an extremely minute component including 320 leads is as input and output terminals. An interval between the leads is 0.25 mm. In addition, such a TCP type IC is relatively small because it does not include any wire-bonded portion that is usually included in ICs. Accordingly, it is possible to fabricate smaller printed circuit boards (PCBs) using the TCP type ICs.
Various earlier methods for soldering and mounting the TCP type ICs including a plurality of leads on the PCB have been provided. One of the methods is an earlier hot bar soldering method using a hot bar. For example, an IC including a plurality of leads formed through a cutting and forming process is placed on a PCB. Then, a heated hot bar is vertically moved down onto the IC. A recessed portion for accommodating a plastic package of the IC is formed in the bottom of the hot bar. Accordingly, when the hot bar is moved down, the bottom sidewalls of the hot bar are brought into contact with only the leads of the IC. At this time, the leads are pressed and soldered on the PCB by the heat of the hot bar.
However, the hot bar soldering method suffers disadvantages in that the leads can be damaged when over pressed by the hot bar, or conductive patterns formed on the PCB can be damaged, which can cause defects, such as a broken pattern due to high temperature of the hot bar. Furthermore, in the event that the leads are soldered under the condition that the leads are caused to slide on the PCB and come in contact with adjacent leads due to the pressure of the hot bar, defects can also be caused.
For efficient soldering, the PCBs are formed as a PCB array integrating four PCBs as a single body. The ICs are successively soldered on the PCB array by the heated hot bar. When the ICs are soldered on the first and the second PCBs, lead melted by the high temperature of the hot bar can adhere to the hot bar. This can result in poor soldering on the third and the fourth PCBs.
To overcome such disadvantages of the hot bar soldering, an earlier light beam soldering method has been provided. In the light beam soldering method, an IC is soldered by applying a xenon (Xe) light beam thereto from a predetermined distance for a predetermined amount of time. The Xe light beam generates a high temperature of 300 degrees centigrade. ICs including a plurality of leads formed through a cutting and forming process are respectively placed on a PCB array including four PCBs. The PCBs are transferred to a predetermined soldering position by a conveyor belt. Thereafter, a holding block is transferred to and vertically moved down onto an IC by a pickup.
Then, in the earlier light beam soldering method, the IC is covered by the holding block. The holding block functions to protect the plastic package of the IC from the heat of the light beam when the light beam is uniformly applied to the whole surface of the PCB as well as the leads to be soldered. The holding block has a structure that only comers thereof are extended downward. Accordingly, when the holding block covers the IC, only the leads of the IC are exposed. The light beam is continuously applied to the PCB with the holding block covering the IC. As a result, the IC is soldered on the PCB. After a predetermined amount of time, the holding block heated to a high temperature is vertically moved up to a predetermined position. In the same manner, the other ICs are soldered on the other PCBs of the PCB array.
However, the earlier light beam soldering method also suffers certain disadvantages. The holding block is heated to a high temperature while it covers the IC for the light beam soldering. Consequently, a predetermined amount of time is required to cool the heated holding block for another light beam soldering. Thus, a period of time is needed between each application of the soldering process. This results in an increased soldering time and a reduced operation efficiency. Moreover, when the time for cooling the holding block is considered, a xenon lamp cannot be used because the xenon lamp emits a great amount of heat. If the xenon lamp is not used, the time for applying a light beam is typically increased. For a practical process, approximately 24 seconds is taken to solder a PCB using the earlier light beam soldering method.
U.S. Pat. No. 4,346,514 to Makizawa et al. entitled Apparatus For Mounting Electronic Components, disclose an apparatus for mounting electronic components on a printed circuit board substrate. The apparatus is disclosed as including a component feeder for sequentially feeding the electronic components in an aligned row, a chuck which receives and rectifies by pinching the position of the electronic components, a vertically movable mounting head, which holds by air suction one of the electronic components preliminarily pinched and rectified of the position by the chuck, and goes downthrough a wide open gap of the chuck to mount the electronic component on an accurate position on the substrate.
U.S. Pat. No. 4,696,104 to Riccardo et al. entitled Method And Apparatus For Placing And Electrically Connecting Components on A Printed Circuit Board disclose a system for placing, soldering and inspecting component parts, such as soldered joints and electronic components, on a printed circuit board which utilizes a transfer device for selecting and transferring specific electronic component parts to predetermined positions on a printed circuit board and holding each component part in the desired position by use of the transfer device during a reflow soldering operation to mechanically and electrically connect the component part to the printed circuit board. It is disclosed that the reflow soldering utilizes a laser beam for injecting thermal energy into each soldered joint to melt the soldered material. An infrared detector is disclosed as sensing thermal radiation and/or reflected radiation from the heated solder material to discontinue the application of the laser beam to the solder material upon liquifaction of the solder material. The infrared detector also continues to sense the thermal radiation from the heated solder material during cool down to provide a signal which will be compared with a standard signal to determine the quality of the solder joint.
U.S. Pat. No. 4,829,665 to Kabeshita et al. entitled Method And Apparatus For Mounting Electronic Components, disclose in mounting electronic components from an electronic components pack to a substrate, the substrate is put on a table movable horizontally in X-Y directions, and the electronic components are held in through holding holes in a holding plate. It is disclosed that a selected one of the electronic components is positioned just above a mounting position on the substrate and a pushing pin is positioned just above that electronic component, the pushing pin lowers and pushes the selected electronic component down out of its holding hole to mount it directly onto the substrate.
U.S. Pat. No. 5,240,170 to Nishida et al. entitled Method For Bonding Lead Of IC Component With Electrode disclose a method for bonding leads of an IC component with electrodes of a circuit board. It is disclosed that the method includes the steps of using a mounting device to hold the IC component with flat portions of the leads inclined downward, mounting the IC component on the circuit board at a predetermined position thereof with the IC component held by the mounting device, moving the mounting device toward the circuit board to compress the IC component against the circuit board at the predetermined position while allowing the leads to flex to accommodate for nonuniformity in the heights of metal pieces to be bonded with the electrodes and bending of the circuit board. In this manner, it is disclosed that the flat portions of the leads are brought into close contact with the electrodes. It is disclosed that the leads are then irradiated with an optical beam so as to melt the metal pieces of the electrodes for bonding of the leads to the circuit board.
U.S. Pat. No. 5,501,005 to Onitsuka entitled Mounting Device Of Electronic Components And A Mounting Method discloses in an apparatus for mounting electronic components, punched out from film carriers to a substrate, there is disclosed an upper die for punching the electronic components through a hole formed in a lower die. A take out nozzle is located under the through hole for sucking the punched out electronic component from the hole in the lower die. A transfer nozzle is provided for receiving the electronic component from the take out nozzle and for transmitting the electronic component to a substrate mounted on a movable table. It is disclosed before any leadwires of the component are bonded to the electrodes of the substrate, the table is finely positioned to properly align the leadwires and the electrodes.
U.S. Pat. No. 5,579,987 to Lee et al. entitled Semiconductor Package Vertical Mounting Device And Mounting Method disclose a method and apparatus for vertically mounting a semiconductor package. It is disclosed the mounting apparatus has an extended (e.g. rectangular) shape, and is provided with a plurality of spaces adapted to receive and hold vertically semiconductor packages. It is disclosed to mount a semiconductor package in such a manner, the package is first inserted into a space in the apparatus provided therefor and fixedly held there. Next, it is disclosed, a plurality of such semiconductor packages which are so held by the mounting apparatus are positioned on a printed circuit board, and their leads are soldered thereto to complete the mounting process. It is disclosed this facilitates both surface mounting and multi-layer wiring and decreases the potential for poor quality soldering. It is disclosed, in addition, the mounting apparatus is beneficially heat dissipative, which helps to increase the life of a semiconductor package by heat which can cause deleterious thermal stresses.
U.S. Pat. No. 5,682,675 to Hirota entitled Apparatus And Method Of Mounting Electronic Components discloses a PC board that is placed at a specified position by means of a positioning device, and an electronic component to be affixed to a side of the PC board is supplied to a parts holding device by means of a carrying head. It is disclosed the parts holding device holds the electronic component with terminal leads of the electronic component facing to a side of the PC board, and the parts holding device is moved towards the PC board to affix the terminal leads of the electronic component to the side of the PC board. It is thus disclosed that terminals of the electronic component, such as connector, for example, may be automatically mounted to a side of a PC board.
U.S. Pat. No. 5,692,669 to Sakemi et al. entitled Printed Circuit Board disclose a printed circuit board including a plurality of lands onto which a plurality of leads of an electronic component are soldered. It is disclosed that these lands are arrayed in parallel to one another. Each of these lands is disclosed as including a narrow portion basically extending in a longitudinal direction thereof and having a predetermined constant width, and a wide portion protruding laterally from both edges of the narrow portion. Also a soldering method for an electronic component is disclosed including preparing a printed circuit board including a pathway and a land connected with each other, the land including a first portion extending in a predetermined direction thereof and a second portion extending from both sides of the first portion in a direction transverse to a longitudinal direction of the first portion, applying solder on a surface of the land, mounting a lead of the electronic component on the solder, and applying heat to the solder so that the solder is melted and then cooling down the solder, thereby fixing the lead of the electronic component on the land of the printed circuit board, wherein the first and the second portions are rectangular.